1. Field of the Invention
The present invention relates to chemical mechanical polishing (CMP), and more particularly, to a conditioner and a conditioning disk for conditioning a CMP pad, and a method of fabricating, reworking, and cleaning the conditioning disk.
2. Background of the Related Art
Highly integrated semiconductor devices require a sophisticated pattern formation technique, and use a multilayer structure for circuit distribution. This means that the surface structure of these semiconductor devices is more complicated, and step height differences between intermediary layers are more severe.
These step height differences cause many process failures in the semiconductor device fabrication process, for example, in the photolithography process for forming a photoresist pattern on a semiconductor wafer, which comprises the steps of coating the wafer with photoresist, aligning a mask having circuit patterns with the wafer having photoresist thereon, and performing an exposure process and a development process.
In the past, the formation method for precise patterns was easier, because the critical dimension (CD) of the pattern was relatively wide, and the semiconductor devices had fewer structural layers. However, the step height difference is increasing due to the finer patterns and multilayered structure of the modern devices. Therefore, it is more difficult to focus between the upper and the lower position of the step height during the exposure process, and it is also difficult to obtain more precise patterns.
Therefore, in order to reduce the step height difference, a planarization technique for the wafer has become important. A planarization technique such as SOG (Spin On Glass) film deposition has been introduced, or a partial planarization technique, such as etch back or reflow, etc., has been used, but many problems persist. Accordingly, a CMP (chemical mechanical polishing) technique for global planarization has been introduced, wherein the planarization is performed throughout the whole surface of the wafer.
The CMP technique planarizes the wafer surface through both chemical and mechanical reactions, whereby the protrusions existing on the surface of the thin film on the wafer chemically react with a slurry supplied to the wafer, with the surface of the wafer having the device pattern contacting a polishing pad surface. At the same time, the protrusions are planarized mechanically by rotation of a polishing table and the wafer.
Referring to FIGS. 1 and 2, the CMP apparatus 1 comprises a polishing table 10 having a polishing pad 12 made of polyurethane attached thereon, a wafer carrier 20 for fixing and rotating a wafer 16, with the thin film pattern 18 on the wafer 16 contacting the polishing pad 12, a slurry 14 supplied on the polishing pad 12, and a conditioner 22 displaced on the opposite side of the wafer carrier 20 and having a conditioning disk 24 attached thereon for conditioning the polishing pad 12.
In the CMP technique using the CMP apparatus 1, removal rate and planarization uniformity are very important, and these are determined by process conditions of the CMP apparatus 1, and the type of slurry 14 and polishing pad 12 used. In particular, the polishing pad 12 affects the removal rate, which should be properly maintained within a process specification by monitoring the surface state of the conditioning disk 24 of the conditioner 22 which conditions the polishing pad 12, and replacing the conditioning disk 24 when necessary.
Referring to FIG. 3, the conditioning disk 24 has artificial diamonds 26 attached to its surface by a nickel thin film used as an adhesive film 25, and the artificial diamond 26 abrades the surface of the polishing pad 12 which is made of polyurethane and has fine protrusions 27.
While the CMP process is continuously being performed for the wafer 16 on the polishing pad 12 by the supplied slurry 14, by-products 28 entrained in the slurry 14 are deposited between the protrusions 27.
Therefore, the surface of the polishing pad 12 becomes slippery with repeated CMP processing, thereby abruptly decreasing the removal rate for subsequent wafers. In order to restore the required removal rate, and maintain the condition of the polishing pad 12, a conditioning is performed to remove the by-products 28. The conditioning is performed by first placing the conditioning disk 24 with the artificial diamond 26 into contact with the surface of the polishing pad 12, and then, rotating the conditioning disk 24 at a certain speed so as to increase the roughness of the polishing pad 12. Therefore, the film of each wafer planarized during the CMP process is within a certain specification.
The conditioning method for the polishing pad 12 is different for a metallic film CMP than for an oxide film CMP. In the case of metallic film CMP, the conditioner 22 conditions the surface of the polishing pad 12 after the CMP for a wafer is preformed. For the oxide film, the CMP process is carried out by simultaneously performing the conditioning of the polishing pad 12 by the conditioner 22 and the CMP for the wafer.
Referring to FIGS. 4 and 5, the conditioning disk 24 has artificial diamonds 26 of a certain size attached on its surface with a nickel thin film 25 functioning as the adhesive. With the continuously-carried out CMP, the by-product 28 including the slurry 14 also accumulates between the artificial diamonds 26 on the conditioning disk 24 as well as on the polishing pad 12. The abrasion of the artificial diamonds 26 itself as well as the accumulation of the by-products 28 between the artificial diamonds 26 decreases the efficiency of the conditioning for the polishing pad 12.
That is, the conditioning effect of the conditioning disk 24 on the polishing pad 12 changes according to the state of the artificial diamonds 26 on the conditioning disk 24.
The size of the artificial diamonds 26 is approximately 68 xcexcm, with approximately 30 to 40 xcexcm protruding from the nickel thin film 25. As a result, the conditioning disk 24 has a short life time, and frequent replacement of the conditioning disk 24 results in decreased productivity and deterioration of production yield due to increased process failures.
The present invention is directed to providing a conditioning disk for a chemical mechanical polishing (CMP) pad for efficiently conditioning the polishing pad, and a method of fabricating the conditioning disk.
Another object of the present invention is to provide a method of reworking the conditioning disk, and a method of cleaning the conditioning disk to reduce production costs and lengthen the life of the disk by reworking a used conditioning disk.
To achieve these and other advantages and in accordance with the purpose of the present invention as embodied and broadly described, the conditioning disk for a CMP pad is divided into regions according to a size difference of the abrasive grains formed on each region of the body surface of the conditioning disk.
The abrasive grains may be artificial diamonds, which are attached to the regions of the body surface of the conditioning disk depending upon their size, one region having artificial diamonds of size greater than 200 xcexcm, and another region having artificial diamonds of size less than 200 xcexcm. The regions on the body surface of the conditioning disk are preferably formed to be concentric rings forming an inner region and an outer region.
The conditioning disk may be ring-shaped with an opening of a certain area in the center. Preferably, the inner region has artificial diamonds having a size of 200 to 300 xcexcm provided thereon, and the outer region has artificial diamonds having a size of 100 to 200 xcexcm provided thereon.
In another embodiment, the conditioning disk has a cross-shaped portion having an opening in its center with a certain area, and a ring-shaped portion adjacent to outer ends of the cross-shaped portion.
In this embodiment, the first region of the body surface has artificial diamonds having a size of 200 to 300 xcexcm provided thereon, and comprises the surface of the cross-shaped portion and those sections of the ring-shaped portion extending from the outer ends of the cross-shaped portion. The second region has artificial diamonds having a size of 100 to 200 xcexcm provided thereon, and comprises arc-shaped sections of the ring-shaped portion extending between the sections extending from the outer ends of the cross-shaped portion.
In another aspect of the present invention, a conditioner for a chemical mechanical polishing (CMP) pad comprises a bar, one end of which is revolvably installed on a fixed unit, a disk holder fastening device installed on the other end of the bar, a disk holder fixed on the disk holder fastening device, and a conditioning disk fixed on the disk holder, wherein the conditioning disk has a surface on which abrasive grains for conditioning a polishing pad are formed in regions defined by a size difference of the abrasive grains.
The conditioning disk may be ring-shaped having an opening in the center of its body, or the conditioning disk may have a cross-shaped portion having an opening in its center, and a ring-shaped portion adjacent to outer ends of the cross-shaped portion.
In another aspect of the present invention, a method of fabricating a conditioning disk of a chemical mechanical polishing (CMP) pad comprises the steps of: a) forming a first adhesive film on the body surface of the conditioning disk with a first thickness; b) attaching abrasive grains to the first adhesive film; c) forming a second adhesive film over the first adhesive film with a second thickness; d) removing incompletely-attached abrasive grains on the adhesive films; and e) forming a third adhesive film over the second adhesive film with a third thickness.
The steps of forming adhesive films may be performed by plating the adhesive film using an electrolytic polishing method. The step of attaching artificial diamonds may be performed multiple times, once on an inner region and once an outer region, the inner and outer regions being concentrically arranged on the surface of the body of the conditioning disk, and being defined according to the size difference of the artificial diamonds attached to the surface in each region.
The thickness of the first adhesive film may be 8 to 10% of a size of the abrasive grain, and the thickness of the second and the third adhesive films may be 15 to 20% of a size of the abrasive grain.
The method preferably comprises a further step of removing incompletely-attached abrasive grains on the adhesive film after the step of forming the third adhesive film. Further, the method may further comprise a step of forming a fourth adhesive film with a fourth thickness after the step of forming the third adhesive film.
In another aspect of the present invention, a method of reworking a conditioning disk for a chemical mechanical polishing (CMP) pad comprises the steps of: a) immersing a used conditioning disk in a chemical in order to dissolve adhesive film and remove abrasive grains attached on the body surface of the conditioning disk; b) cleaning the body surface of the conditioning disk; c) forming a first adhesive film with a first thickness on the body surface of the conditioning disk; d) attaching abrasive grains to the first adhesive film; e) forming a second adhesive film with a second thickness over the first adhesive film; f) removing incompletely-attached abrasive grains on the first and the second adhesive film; and g) forming a third adhesive film with a third thickness over the second adhesive film.
In another aspect of the present invention, a method of cleaning a conditioning disk for a chemical mechanical polishing (CMP) pad comprises the steps of: a) immersing a used conditioning disk in a chemical in order to remove by-products existing between abrasive grains on the body surface of the conditioning disk; b) cleaning the conditioning disk using deionized water; and c) drying the conditioning disk.
The by-products may be mixed compounds of oxide film and slurry, or mixed compounds of metallic film and slurry, and the chemical is HF (hydro fluoric) solution or BOE (buffered oxide etch) solution.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.